High strength alloy steels



United States Patent HIGH STRENGTH ALLOY STEELS Clyde A. Furgason, Milwaukee, Wis., assignor to Ladish Co., Cudahy, Wis., a corporation of Wisconsin No Drawing. Application March 20, 1959 Serial No. 800,663

3 Claims. (Cl. 75-128) This invention relates to improvements in high strength alloy steels and more particularly to a steel suitable for use where ultra-high strength is desirable for weight saving, as well as where high strength must be maintained for prolonged periods of elevated temperatures.

Heretofore low alloy steels, due to temper brittleness, have never been suitable for ultra-high strength applications, and in order to get a low alloy material in strength levels above 180,000-200,000 p.s.i. tensile it has heretofore been necessary to temper in a temper-brittle range where ductility was detrimentally affected.

A general object of the invention is to provide an improved alloy steel which has only a nominal total alloy content whereby it uses only a minimum of strategic ma terials, making it economically desirable.

A further object of the invention is to provide an alloy steel as above described which is capable of being heat treated to ultra-high strength levels while maintaining adequate ductility, particularly transverse ductility.

A further object of the invention is to provide an alloy steel which is suitable for use where superior toughness, wear resistance, elevated temperature strength, and high impact load resistance are necessary, such as in hot work die applications.

A further object of the invention is to provide an alloy steel which exhibits superior properties at room temperature when heat treated to a predetermined high tensile strength range, the alloy retaining sufficient toughness so that it can be used for missile and aircraft structural applications and having excellent elevated temperature properties when heat treated to a predetermined tensile strength range.

A further object of the invention is to provide an alloy steel which maintains a high yield to ultimate ratio at all strength levels up to 280,000 p.s.i. ultimate. 7

Other objects are to provide an alloy steel which exhibits less distortion in quenching, and which is weldable in heavy sections while employing techniques and control normally used in welding medium carbon low alloy materials with high hardenability.

A further object of the invention is to provide improvements in the processing of an alloy steel of the class described.

In carrying out the invention it has been discovered that a relatively high carbon range can be' used in the formula without causing brittleness while the product maintains ductility and good weldability.

The alloy of this invention has the following contents in percent: I

Remainder iron with incidental impurities.

It is important to maintain the phosphorous and sulphur content-relatively low. The nickel content is always 2,919,188 Patented Dec. 29, 1959 less than chromium content and is always less than the molybdenum content. A small amount of vanadium may be used to control the grain size, this amount, however, being kept so low as not to affect the essential properties of the alloy.

A desirable formula for many purposes is:

Remainder iron with incidental impurities.

The above formula may be modified by the addition of other elements and the present invention is not to be construed so as to preclude the use of small amounts of such additional elements as vanadium, suggested above, uranium 238, boron, or rare earth elements in the basic composition.

It is apparent from the above tables that the alloy content is very low so that only a minimum of strategic materials need be employed to obtain properties heretofore obtained only by a much higher alloy content.

In manufacturing the improved alloy, alloying agents are added at the steel mill in accordance with the above formula, except that when there is to be a vacuum arc consumable electrode remelt the amount of manganese is chemically adjusted at a higher level, for example, between .95-1.20 to allow for losses. While an air melt process produces a satisfactory alloy, transverse ductility and other properties can be substantially improved by use of a vacuum arc consumable electrode remelt furnace process. When this process is used the alloy after being through an air melt process and in ingot form is rolled to billet form to fit a consumable electrode furnace in the mill. It is then remelted in a vacuum arc consumable electrode remelt furnace and during such remelting it losses the excess manganese to provide a final manganese content like that listed in the formula above. The vacuum arc consumable eelctrode remelt furnace has a purging eifect on lighter impurities, which can then be eliminated, so that the number and size of the impurities from the air melt are greatly reduced. Those impurities which remain are smaller and better distributed. As a result, the alloy is much cleaner and has improved transverse ductility and other properties.

The following tables indicate the improved properties of the alloy steel of the present invention:

TABLE A Mean coeflicient of thermal expansiom IN. PER IN. PER F. 10

CM. PER CM. PER C. X10

TABLE B Modulus of elasticity Test temperature: Modulus of plasticity 80 F. 30.5)(10 400 F. 24.4)(10 500 F. 24.9)(10 600 F. 25.7 10 700 F. 252x10 800 F. 237x10 900 F. 23.8 1000 F. 232x10 1100 F. 15.7 10 1200 F. 11.1 10

TABLE C Mechanical properties at room temperature 2% 112% Percent Percen Charpy Temper U.S., Y.S., Y.S., Elong. Red. V-Notch Temp., F. p.s.i p.s.1. p.s.i. in 2 of Impact,

inches Area ft. lb.

(Average of 8 Heats) This table shows that the maximum ultimate tensile strength and yield strength, which is indicative of adequate ductility, is achieved by tempering at SOD-700 R, which temper produces approximately 260,000285,000 p.s.i. tensile strength, approximately 240,000255,000 p.s.i. yield strength, approximately 9.0-11.0% elongation, and a Charpy V-notch impact of approximately ft. lbs.

4 TABLE E Evolution of sheet material [Sheet product-0.100 thick-tested after surface removal] LON GI'IUDIN AL Yield Elonga- Ultimate Strength tion, per- Temper Temperature, F. Strength, (.2 0 cent in 2 p.s.i. Oflset), inches p.s.i.

Evolution of welded sheet F. Normalize 1, 650 Air Quench- 1,550 Temper. 600

Ultimate Yield Elongation Elongation Strength, Strength in 1, in 2",

psi. (.2% Otiiset), percent percent;

TABLE F Room temperature mechanical properties when remelted under vacuum by the consumable electrode process [Mechanical properties of present alloy steel at room temperature. Normalized 1650" F., air quenched 1550 F., tempered at 600 F.]

, Tensile Yield Elong. Red. of Heat Test Direction Strength, Str. 2% percent Area,

N o. p.s.i. Ofiset, in 2 percent p.s.i. inches 1 {Longitudinal. 275, 875 248, 500 8.8 37. 0 Transverse" 275, 745 246, 821 7. 5 15. 8 2 {Longitudinal 277, 000 247, 500 10. 0 38. 8 Transverse. 277, 250 246, 000 6. 0 17. 5 3 {Longitudinal 284, 000 255, 000 9. 5 34. 4 Transverse. 284, 650 255, 750 6. O 19. 6 4 {Longitudina 281,025 250, 975 7. 8 31. 0 Transverse" 279, 376 250, 688 6. 3 19. O 5 {Longitudinal. 283, 500 257, 750 9. 3 37. 6 Transverse" 274, 313 246, 313 5. 4 15. 3 6 {Lougitudinal 280, 000 253, 500 9. 9 41. 5 Transverse..- 280, 588 253, 963 6. 4 21. 9 7 {Longitudinal 280, 625 253, 250 8. 5 29. 6 Transverse 279, 876 251, 438 6. 24. O 8 {Longitudinal. 283, 950 258, 950 8. 0 31. 9 Transverse 281, 388 256, 263 5. 3 19. 3 9 {Longitudinal 294, 300 265, 200 8.0 29. 7 Transverse"- 285, 550 258, 963 5. 0 15. 7

This table shows the high transverse ductility. (Nora- Transverse tensile test results are average of four specimens.)

Short time elevated temperature properties of the present product, when tempered at 50 F. above the test temperature, are summarized in Table G below. Test temperatures are 50 F. below corresponding temper temperatures to simulate treatment necessary to be compatible with operating temperatures; i.e., tempering temperature must be higher than operating temperature to prevent tempering of the material while operational. The data shows the product to have superior high tensile strength at elevated temperatures. Since the yield strength is well above 140,000 psi at 900 F., the present product is desirable for many elevated temperature structural applications. This data is indicative of properties obtainable when designing to operating temperature ranges.

TABLE G Short time elevated temperature properties lNormalize 1650 F., oil quench 1550 F., tempered 50 F., above the test temperature average of 5 tests] Ultimate Yield Elong. Bed. of Test Temperature, F. Strength, Strength in 2", Area,

p.s.i. (0.2% on Percent Percent set), p.s l

Correspondzng room temperature propertles Ultimate Yield Elong Bed. of Tampering Strength, Strength in 2", Area, Temperature, F. p.s.i. (0.2% On Percent Percent set), p.s I

In addition to the above, the material has impact properties which are fairly uniform when tested at elevated temperature and are consistent with room temperature values obtained from specimens treated to the same strength level. In addition, the material has desirable low temperature impact properties, elevated temperature stability, excellent stress rupture properties up to 900 F., test temperature, giving the alloy definite advantages in applications where there are heavy loads and high temperatures for prolonged periods of time. In addition, the alloy steel has desirable notch tensile properties even when heat treated to ultra-high strength. Also, the strained tensile test shows a marked increase in tensile strength and a definite raise in the yield to ultimate ratio 1 from .94.99 at 600 F. temper over unstrained tests treated similarly.

010% phosphorous, up to about 010% sulphur, and the remainder being iron with incidental impurities, and the metal being characterized by its ability to maintain high strength considering its low alloy content for prolonged periods of elevated temperatures with accompanying good ductility, there being an absence of temper brittleness when tempered at low tempering temperatures, and the metal being characterized by low temperature properties and a very low transition temperature when treated to very high strength levels.

2. An improved alloy steel which contains approximately .46% carbon, about 58-93% manganese, about 13-32% silicon, about 35-75% nickel, about .87- 1.23% chromium, about .88-1.12% molybdenum, up to about 010% phosphorous, up to about 010% sulphur, up to about .10% vanadium, and the remainder being iron with incidental impurities, and the metal being characterized by its ability to maintain high strength considering its low alloy content for prolonged periods oi elevated temperatures with accompanying good ductility, there being an absence of temper brittleness when tempered at low tempering temperatures, and the metal being characterized by low temperature properties and a very low transition temperature when treated to very high strength levels.

3. An improved alloy steel which contains about .40- .50% carbon, about .58.93% manganese, about .13- 32% silicon, about .35-.75% nickel, about .87-1.23% chromium, about .881.12% molybdenum, up to about .010% phosphorous, upto about .010% sulphur, up to about .10% vanadium, and the remainder being iron with incidental impurities, and the metal having been remelted in a vacuum arc consumable electrode remelt furnace and being characterized by its ability to maintain high strength for prolonged periods of elevated tempera tures and having high transverse ductility with an absence of temper brittleness when tempered at low tempering temperatures, and the metal being characterized by low temperature properties and a very low transition temperature when treated to very high strength levels.

References Cited in the file of this patent Dyrkacz et al.: Arcs in Inert Atmospheres and Vacuum, 1956, pages 97-111. Edited by W. E. Kuhn and published by John Wiley & Sons, Inc., New York, N.Y.

Super-High Strength Steels for Aircraft Applications, reprinted from Proceedings of the 1955 Sagamore. Research Conference, Ordnance Corps, US. Army. Published by The International Nickel Co., Inc, New York, N.Y.

Ultra-Strength Steels, 1957. Pamphlet published by Climax Molybdenum Co., New York, N.Y. 

1. AN IMPROVED ALLOY STEEL WHICH CONTAINS ABOUT 40-50% CARBON, ABOUT .58-93% MANGANESE, ABOUT 13-32% SILICON, ABOUT .35-75% NIXKEL, ABOUT 987-1.23% CHROMIUM, ABOUT .88-1.12% MOLYBDENUM, UP TO ABOUT 0.10% PHOSPHOROUS, UP TO ABOUT 0.10% SULPHUR, AND THE REMAINDER BEING IRON WITH INCIDENTAL IMPURITIES, AND THE METAL BEING CHCRACTERIZED BY ITS ABILITY TO MAINTAIN HAGH STRENGHT CONSIDERING ITS LOW ALLOY CONTENT FOR PROLOINGED PERIODS OF ELECATED TEMPERATURES WITH ACCOMPANYING GOOD DUCTILITY, THERE BEING AN ABSENCE OF TEMPER BRITTLENESS WHEN TEMPERED AT LOW TEMPERING TEMPERATURES, AND THE METAL BEING CHCRACTERIZED BY LOW TEMPERATURE PROPERTIES AND A VERY LOW TRANSITION TEMPERATURE WHEN TREATED TO VERY HIGH STRENGTH LEVELS. 